Re: [Detnet] [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

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Hi Greg,

Please see inline [Bruno2]



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From: Greg Mirsky <[e-mail]>
Sent: Thursday, March 31, 2022 5:48 PM
To: DECRAENE Bruno INNOV/NET <[e-mail]>
Cc: Tony Li <[e-mail]>; mpls <[e-mail]>; detnet WG <[e-mail]>; Andrew G. Malis <[e-mail]>; [e-mail]
Subject: Re: [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

Hi Bruno,
thank you for the expedient response to my notes. Please find a follow-up in-lined below under the GIM>> tag.

Regards,
Greg

On Thu, Mar 31, 2022 at 12:59 AM <[e-mail]<mailto:[e-mail]>> wrote:
Hi Greg,

Please see inline [Bruno] tentative replies to your questions.



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From: Greg Mirsky <[e-mail]<mailto:[e-mail]>>
Sent: Wednesday, March 30, 2022 9:48 PM
To: DECRAENE Bruno INNOV/NET <[e-mail]<mailto:[e-mail]>>
Cc: Tony Li <[e-mail]<mailto:[e-mail]>>; mpls <[e-mail]<mailto:[e-mail]>>; detnet WG <[e-mail]<mailto:[e-mail]>>; Andrew G. Malis <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Pals] [mpls] draft-decraene-mpls-slid-encoded-entropy-label-id (was RE: Please review the PALS/MPLS/DetNet Joint Session minutes)

Hi Bruno, et al.,
I have several questions and would greatly appreciate your thoughts:

  *   Do you see the need for extensions to the routing protocols that now advertise the support of RFC 6790 to avoid the scenario that John has pointed out?
[Bruno] No and so far I'm not even seeing any (negative) scenario in John's email.
GIM>>  I hope you can point me to the verbiage in RFC 6790 that supports the following statement in your draft:
   Hence essentially the TTL field of the EL behaves as a reserved field
   which must be set to zero when sent and ignored when received.
I can only find the following text in Section 4.2 RFC 6790:
       The TTL for the EL MUST be zero
       to ensure that it is not used inadvertently for forwarding.
which says nothing about ignoring the EL TTL field value. Quite the opposite, my understanding is that the value must be checked, and if it is non-zero, the packet must be discarded. Based on that, I don't see how the extended interpretation of ELI can be safely deployed without any extensions in the control plane.

[Bruno2] Your understanding is incorrect. And yes I can point you to the text in RFC 6790 saying that the value must not be checked.

"The EL's TTL MUST be ignored." https://datatracker.ietf.org/doc/html/rfc6790#section-4.1



  *   As I understand the draft, using EL and Slice ID in the same stack is mutually exclusive. If that is the case, how entropy can be created within the particular network slice?
[Bruno] Please reread the draft and more specifically sections 3 and 3.1. You are not correct: the use of EMCP entropy and slice ID is not mutually exclusive, in the stack but even in a single EL. In short, one part of the EL is used to encode the slide ID and the remaining part carry the entropy number. Legacy transit LSR may use the whole EL transparently as the whole EL _is_ an entropy value which may be used for load-balancing (how that EL value is constructed by the ingress is not the concern of the transit).
GIM>> Thank you for clarifying this use case for me. As that is the case, I believe that there's even more reason for extensions in the control plane to signal how the EL field is used.
[Bruno2] I don't share your believe but I don't think that this point is the key one so I'd propose to skip it.

  *   I think that you've agreed that the draft does not address the requirements for MIAD<https://datatracker.ietf.org/doc/draft-bocci-mpls-miad-adi-requirements/>. You've pointed out Jags' draft<https://datatracker.ietf.org/doc/draft-jags-mpls-ext-hdr/> as the possible solution that is based on the re-definition of the ELI and may address MIAD ADI requirements, To that, I can make two observations:

     *   re-using ELI is only one optional approach discussed in draft-jags-mpls-ext-hdr. I think that is not guaranteed that that would be the option used if the document is published.
     *   And if draft-jags-mpls-ext-hdr continues with the solution based on the re-definition of the ELI, it appears to me that all Tony's concerns are valid.
[Bruno] I'm not sure what anything new your are bringing in addition to Tony's analysis and email. So I'll just copy past the same reply:
There are two steps:
- This proposal allows for carrying 8 Indicators and a slice ID while been backward compatible with egress LER hence providing faster deployment with incremental benefit.
GIM>> As I don't agree with your assumption that EL TTL value must be ignored and thus can be re-used for ADIs. I find that there are only three flags that can be safely used with your proposal. And that is without any ISD support.
[Bruno2] Do you know agree that the EL TTL field must be ignored? If so your point is moot.

--Bruno
- If more in-stack data is required the proposal is extensible (e.g. draft-jags-mpls-ext-hdr) but at the cost of losing the above benefits for the ASes & uses-cases requiring more than 8 Indicators per AS or In-Stack Data.
So we can have both worlds: simple first step and extensibility for those who need it.

Thank you in advance for your consideration of my notes.
[Bruno] You are very welcome. Thank you in advance for considering my answers.

Regards,
Bruno
Regards,
Greg

On Wed, Mar 30, 2022 at 9:59 AM <[e-mail]<mailto:[e-mail]>> wrote:


From: Tony Li <[e-mail]<mailto:[e-mail]>> On Behalf Of Tony Li
Sent: Wednesday, March 30, 2022 4:08 PM
> [Kireeti]: suggest attending talk by Tony on danger of reusing ELI before making any decision.
https://notes.ietf.org/notes-ietf-113-pals

Done. The talk raised no "danger of reusing ELI" for draft draft-decraene-mpls-slid-encoded-entropy-label-id; quite the contrary.
I quote: "claims of backward compatibility apply to draft-decraene-mpls-slid-encoded-entropy-label-id-03". With more details on slide 18
https://datatracker.ietf.org/meeting/113/materials/slides-113-mpls-05-policy-on-mpls-special-purpose-labels-reuse-00


Yes, the issue with this proposal is that it has no space for in-stack data and not enough space for possible expansion of additional actions.

[Bruno] There are two steps:
- This proposal allows for carrying 8 Indicators and a slice ID while been backward compatible with egress LER hance providing faster deployment with incremental benefit.
- If more in-stack data is required the proposal is extensible (e.g. draft-jags-mpls-ext-hdr) but at the cost of losing the above benefits for the ASes & uses-cases requiring more than 8 Indicators per AS or In-Stack Data.
So we can have both worlds: simple first step and extensibility for those who need it.

Independently, we also/already have the post stack data option to carry ancillary data, which may limit the need for In-Stack data extension.

--Bruno

Tony




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